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Murray hardyhead - Craterocephalus fluviatilis
McCulloch, 1913 (Atherinidae)
By Brendan Ebner and Tarmo Raadik
Threatened Fish Profile – In Newsletter 31_2, December 2001
Photo: Michael Hammer
Conservation status: Vulnerable (ANZECC 2000); Endangered (ASFB 2001).
Description: A moderately deep-bodied atherinid of small size (max. 72mm), body often predominantly luminescent silver in adults with a silver midlateral stripe (Ivanstoff and Crowley 1996) although fins are coloured bright orange at spawning.
Distribution: Endemic to lowlands of the Murray and Murrumbidgee River Systems but not the Darling River in south-eastern Australia. Collected as far upstream on the Murray River as Yarrawonga (36o 01′ 146o) and as far downstream as Lake Alexandrina at the Murray Mouth (35 o 30′ 139 o). Initially collected from the Murrumbidgee Catchment where the current distribution is unknown. Species has most commonly been found in slight to highly saline waters, in particular ephemeral deflation basin lake systems near Kerang and Mildura, Victoria and the Riverina district of South Australia.
Historically the species has been confused with a number of species including C. eyresii, C. amniculus and C. stercusmuscarum fulvus (Crowley and Ivanstoff 1990 However, only the latter species is also found in the southern tributaries of the Murray-Darling Basin (Ivanstoff and Crowley 1996).
Abundance: Sometimes abundant in certain ephemeral deflation basin lakes, although subject to seasonal fluctuations in abundance (Raadik and Fairbrother 1999; Ebner Pers. Obs.). Populations in some lakes appear to have declined or been eliminated (e.g. Hardie 2000).
Habitat and ecology: Craterocephalus fluviatilus appears able to complete its entire life cycle in ephemeral deflation basin lakes. A highly mobile, schooling fish that inhabits open-water, often over very shallow sandy flats but also known from deeper, well vegetated areas, under conditions of temporary or permanently elevated salinity and reduced turbidity. Currently, a population in Lake Elizabeth tolerates salinities well above that of seawater (48 000μS/cm, Hardie 2000). Diet consists primarily of microcrustaceans (Hardie 2000; Ebner Unpubl. Data). Adults with mature gonads have been collected in November (Raadik and O’Connor 1996; Raadik and Fairbrother 1999) and the species is probably a phytophilic spawner. Newly hatched specimens as small as 5mm TL have been collected from the Cardross Lakes in mid summer (Ebner Unpubl. Data). Note the study of Llewellyn (1979) pertains to reproduction of C. stercusmuscarum fulvus not C. fluviatilis (see Crowley and Ivanstoff 1990).
Threats and Conservation: Salt diversion into ephemeral deflation basin lakes poses an immediate threat to several Victorian C. fluviatilis populations. The species is at risk to the large-scale effects of river regulation in the form of altered connectivity between ephemeral deflation basin lakes and the Murray River. The species has received limited attention from a conservation viewpoint. A priority should be to comprehensively survey the distribution of the species in ephemeral deflation basin lakes, and near by habitats, especially in New South Wales. The basic ecology of the species including population response to the wetting and drying regimes in lakes needs investigating as several populations exist in regions of extensive irrigation development. Furthermore, the occurrence of high rates of spinal deformity in Lake Hawthorn and Cardross Lakes populations requires research attention.
Current Research: Very little research has been conducted on this species. Currently, the distribution of C. fluviatilis is being distinguished from that of C. stercusmuscarum fulvus in the southern Murray-Darling Basin based on reidentification of specimens derived from opportunistic collections by several researchers. Initial results suggest the two species are rarely sympatric and that C. fluviatilis commonly inhabits slightly saline waters, particulalry ephemeral deflation basin lakes.
Further Information:
Brendan Ebner, Wildlife Research and Monitoring,
PO Box 144, Lyneham ACT 2602,
Ph: (02) 6207 2119
E-mail: brendan.ebner@act.gov.au
References:
ANZECC. 2000. Threatened fauna list. Environment Australia, Canberra.
ASFB. 2001. Conservation status of Australian Fishes (provisional list). Australian Society for Fish Biology, INC. Newsletter 31(1): 37-40
Crowley L.E.L.M. and Ivanstoff W. 1990. A review of species previously identified as Craterocephalus eyresii (Pisces: Atherinidae). Proc. Linn. Soc. N.S.W. 112: 87-103
Hardie S.A. 2000. Examination of fish and invertebrate fauna in seven lakes in the Swan Hill – Kerang region, Northern Victoria. Natural Resources and Environment.
Ivanstoff W. and Crowley L.E.L.M. 1996. Family Atherinidae. Silver sides or hardyheads. In: McDowall R.M. (Ed) Freshwater fishes of south-eastern Australia. p123-133
Llewellyn L.C. 1979. Some observations on the spawning and development of the Mitchellian freshwater hardyhead Craterocephalus fluviatilis McCulloch from inland waters in New South Wales. Aust. Zool. 20: 269-288
Raadik T.A. and Fairbrother P.S. 1999. Cardross Lakes aquatic fauna monitoring – November 1998. Freshwater Ecology Parks, Flora and Fauna. Arthur Rylah Institute for Environmental Research, 123 Brown St, Heidelberg VIC 3084.
Raadik T.A. and O’Connor J.P. 1996. Third aquatic fauna survey (fish and decapod crustacea) of Cardoss Lakes near Mildura, Victoria. Report for Cardross Lakes Task Group, North West Area, Department of Natural Resources and Environment (State Public Offices, 253 Eleventh Street, Mildura